Hi - I am using an air sourced heatpump to heat my Intex above ground pool. Last year the pool heater worked well but this year I can't get enough water flow to start the heater. I have bought a new circulation pump (a 3/4 HP one - much bigger than is needed). I can hear some air in the system near to the heater but can't get rid of it. Any suggestions would be really appreciated, many thanks.